Process of producing pure aluminum hydrate particularly from aluminum-containing raw materials rich in silica



ll atente ct. 22, 1929 ERTK LUDVIG ETNMAN, 01E IDLl'UlBLSHULM,

MINUlVlI-CUNTAINING RAW MATERIALS; ltIIUl-lt llhl' tlllllltlfll.

Llto Drawing, application filed November 14, 1925, serial lilo. outer, and in ttweden lilovcmher as, l tl,

The present invention relates to a process of producing pure aluminum hydrate. The present process is particularly adapted for the production oi such hydrate from raw materials rich in aluminum oi? the kind which owing to their high percentage of silica can not suitably be treated according to lBayers soda l e process, but the process may of course also lie utilized for the treatment oil:

n raw materials poor in silica.

The process consists principally in that trom the aluminum-containing raw mate rial an aluminum sulphate solution is first produced according to well-hnown methods,

and in this conection it is to be observed that high percentage o'l iron in said solution does does not render the following operations more diticult in a degree worth men tioning, The said solution is atterwards as mixed, preferably in a hot state, with a solution oi? sodium sulphydrate, which may contain sodium sulphide, and which is also prelerably in a hot state, in approximately such quantities that all aluminum is precipitated as as hydrate, while liberating hydrogen sulphide which latter may be taken care of separately. Atterwards the aluminumhydrate thus obtained, which possibly contains iron, is separated from the sodium sulphate solution and the sodium sulphydrate possibly remaining in said solution, so that an aluminum hydrate tree "from sulphuric acid to the desired degree is obtained.

in order "from this impure aluminum hy 3 drate to produce ure aluminum hydrate the following course is adopted, according to the invention 2 The impure aluminum hydrate is dissolved in. a solution oil sodium sulphide so as to form til sodium aluminate and sodium sulphydrate, after which the undissolved residue of Fed and other impurities is separated, and the mixed sodium aluminate and sodium sulphydrate solution thus obtained is treated, pref- 4 erably in a hot state, with hydrogen sulphide. All aluminum hydrate is then precipitated, provided that a sufficient quantity of hydrogen sulphide gas is introduced. The hydrate thus precipitated is afterwards separated from the sodium sulphydrate solution by filtration and washing, so that pure aluminum hydrate is obtained, The sodium sulphydrate solution thus obtained may atterwards be used for precipitating impure aluminum hydrate from an aluminum sulphate solu-- tion in the manner above described. Th reactions take place according tothe toll ing formulae, the iron in the clay, and M and GU, in the sodium sulphide solution being disregarded:

amour, amuse, ems. muons3 2mm: amino, amen an o. amino, fangs QllllSH 2H 0=2A10 l5t mass. 3Il 92 602 2 tsna so, cc: snags econ.

Theoretically, the chemicals used in this process may thus be completely recovered, but in practice there will o'lt course be some losses. lit there is iron present in the aluml" num sulphate solution, such iron. will be obtained in the state oil held, from which the sulphur may be recovered, however, by burn ing, in the state oil ill), from which ldhfiotl may be produced. lin practice, sulphuric acid will, of course, be lost, w ich quantity is suitably replaced by purchased acid, or by sulphur dioxide or sulphuric acid produced by burning sulphur or pyrite, Elm

dium lost is suitably replaced by sodium sulphate.

lln order to illustrate the invention an em ample oil the manner in which the present process may be carried out, is described here below. It is assumed that ordinary clay "tree from lime is used as raw material. llln the other hand, the clay assumed to contain iron. From said clay an aluminum sulphate solution is first produced, by treating the clay in well-known manner with sulphuric acid, so that an aluminum sulphate solution approximately 100 C. hot is obtained, the concentration of which corresponds to saturation at about G, and the percentage out iron of which with relation to iltl O, may amount to Spercent Fefl or more. I

it measured quantity of the abovementioned aluminum sulphate solution, approximately C. hot, is pumped through one or more pipes into a measured solution of sodium sulphydrate,

also 100 C. hot, which I tilt till

ill

a quantity oil lit ' is estimated in such manner that for each molecule SO in the sulphate solution there are two molecules NaSH in the sodium sulphydrate solution, preferably with a slight excess of NaSH so that all aluminum will be completely precipitated as hydrate. The sodium sulphydrate solution may also contain some sodium sulphide, if desired. During this process the sodium sulphydrate solution is preferably maintained in a lively movement, for instance in an ordinary closed mixing apparatus. During the process a quantity of H 8 equivalent to the quantity of sulphuric acid is given off in gaseous state. A precipitate of Alon FeS Na 0.Al 0 .SiO2 eazo etc. is formed, and in the solution Na,SO all in equivalent quantities. and the solution also contains the excess of Na SH. The hydrogen sulphide is drawn off in order partly to be used for the purpose below specified, and partly to be transformed into sulphuric acid by burning in well-known manner, for the purpose of supplying the greater portion of the quantity of such acid required in the process. The aluminum hydrate precipitate obtained in this manner is very easily filtered, provided that the aluminum sulphate solution was introduced in the sodium sulphydrate solution, and not vice versa. so that it is possible to use, practically speaking. all conceivable filtering devices for separating the precipitate from the sodium sulphates lution. Since, however, itis not particularly important to wash away completely all sodium'sulphate from the precipitate, the filtration and washing mav suitablv be effected by means of continuously operating, for instance rotary, filters. The sodium sulphate solution thus obtained is evaporated, and the sodium sulphate obtained is reduced,

,; mixed with a further quantity of sodium sul- 'phate if desired, to

' cally.

make up for the losses in the manufacture; so that sodium sulphide is againobtained, which is again introduced into the process in an operation below de scribed.

The aluminum hydrate precipitate obtained by the filtration. and which contains iron sulphide and possibly also sodium sulphate, is afterwards dissolved. for instance in a closed mixing apparatus, which should preferably be provided with a heating device for direct steam, and which contains sodium sulphide solution at a temperature of about 100 C. The solution is maintained at the boiling point, or above the same, as long as alummum hydrate is dissolved. Theoretithere would only be required for such dissolution such quantity of Na s-solution that for one molecule A1 0 there are two molecules-Na s.

Owing to the fact, however, that as a rule the Na S-solution contains some carbonate and sulphate and owing to the fact that there is not formed NaAlO exclusively, but as a rule also some Na O Al, some more sodium sulphide solution should be used, as a rule probably three molecules Na s, that is to say, the entire quantity of sodium sulphide that according to the formulae is theoretically required for carrying out the process, and which quantity will thus circulate, so to speak, in this manufacture. WVhen all aluminum that can be dissolved, has been dissolved, the undissolved iron sulphide and other impurities are filtered away, and the filtrate thus obtained is precipitated at a temperature of about 100 C. by the introduction of hydrogen sulphide gas, preferably such gas as has been obtained in a preceding operation. As soon as in this manner all aluminum has been precipitated as hydrate, the operation is read The precipitated aluminum hydrate, which is particularly easily filtered, is afterwards completely separated from the sodium sulphydrate solution by filtration and washing, for instance in suction filters or pres sure filters. The washing, which should preferably be effected with hot washing liquids and hot water,'is continued-without taking care of the thinnest filtrate, if desireduntil the precipitate becomes chemically free from sulphur. The aluminum hydrate thus produced has now obtained a sufficient purity, for instance for the production of pure aluminum oxide. For this 'it is of course a condition that the sodium sulphide solution used is of the desired purity. Carbonate possibly present in the sodium sulphide solution may of course be removed to the greater part by causticizing with lime and subsequent filtering away of the precipitated carbonate.

The sodium sulphydrate solution obtained in this operation is utilized in the manner above described for the production of aluminum hydrate from the aluminum sulphate solution, and so forth. Theoretically there would only be required for the precipitation of the pure aluminum hvdrate with H 8 twofifths of the quantity formed at the first precipitation of aluminum hydrate, but in practice there will probably be required up to about half of said quantity.

It will be obvious to those skilled in the art that all sodium compounds used in the present process may be replaced by the cor responding potassium compounds, and the term sodium used in the claims should therefore be understood as being equivalent to potassium.

I claim:

1. The process of producing pure aluminum hydrate, particularly from aluminumcontaining raw materials rich in silica, which consists in treating the aluminum-containing raw material with sulphuric acid for producing aluminum sulphate solution, treating said aluminum sulphate solution with sodium sulphydrate solution for producing impure till a r/sauna aluminum hydrate and sodium sulphate and hydrogen sulphide, separating said sodium sulphate and hydrogen sulphide from said impure aluminum hydrate, dissolving said impure aluminum hydrate in sodium sulphide solution so as to form sodium aluminate and sodium sulphydrate, filtering oft undissolved residue and precipitating pure aluminum hydrate from the mixed sodium aluminate and sodium sulphydrate solution ohtained by treating said solution with hydrogen sulphide and separating such pure aluminum hydrate from the sodium sulphydrate solu tion formed.

2.. 'llhe process according to claim 1, in which the aluminum sulphate solution is treated with sodium sulphydrate solution contraining sodium sulphide. I

3. The process according to claim 1, in which the precipitation of the impure aluminum hydrate from the aluminum sulphate solution is edected in such manner that hot aluminum sulphate solution is introduced into hot sodium sulphydrate solutionJ 4t. The process according to claim 1, in which the precipitation of the pure aluminum hydrate with hydrogen sulphide gas is etl'ected under heat.

5. The process according to claim 1, in which the sodium sulphate solution obtained is evaporated and used for the production of sodium sulphide, which is again used for the manufacture, loss of sodium sulphide heing supplied by sodium sulphide simultaneously produced from further quantities of sodium sulphate.

6. The process according to claim 1, in which the impure aluminum hydrate is dissolved in sodium sulphide solution at a term till perature of substantially 100 C.

ERIK LUDVIG RINMAN; 

